The present invention relates to a panel for picking up or collecting solar energy having reduced losses, especially of the frontal type, and therefore a better efficiency.
It is known, and it is becoming progressively more developed as an alternative source of energy, to utilize solar energy to obtain heating of fluids up to temperatures of about 80.degree. C.
Conventionally this result is attained by collecting plates, for example black or blackened, to absorb solar radiation, and means to remove the heat therefrom, such as a system which circulates a fluid capable of exchanging the heat with the collecting plates and having a good thermal coefficient.
It is also known to improve the efficiency of these systems by forming panels with one or more plates of glass over the absorbing plates to produce a "greenhouse effect" which reduces the heat losses due to radiation from the hottest surfaces.
However, an excessively high number of glass plates overlying the absorbing surface would reduce, due to the unavoidable reflections, the incident energy to the absorber, thus reducing the resulting temperature.
On the other hand, if one tries to obtain higher temperatures through the utilization of indirect focusing of the solar rays (e.g. reflecting mirrors) or a direct focusing (e.g. convex glasses or of a special type such as to so-called Fresnel lenses) a decreased total efficiency is on the contrary met, this also without considering the inherent costs and the complex installation and maintenance operations required. It can be often observed that as the temperature obtained on the collecting plate increases, then efficiency decreases and it is impossible to obtain consistent flow rates of the heated fluid at substantially higher temperatures.
It is in fact known that the installations for the utilization of solar energy hitherto made have been almost exclusively limited to sanitary domestic uses, such as the supply of hot water, without being able to have those industrial applications which are generally desired, so that solar energy could be really considered an alternative and competitive energy source.
It could be stated that up to now the best total efficiency of the solar panels has been obtained through the technique of providing a vacuum therein, between the covering plate and the collecting bottom surface, but the slight improvement obtained does not justify the consequent increases in cost.